Recent projects for transferring Public Office buildings and estimation of appropriate construction expense are highly important for both government and construction firms. Moreover, estimation and management of construction expense can be regarded as extremely important duties for effective execution of a national budget as nation’s finance is invested in the Public office building projects progressed by the government. To progress one project for Public office building, not only the organization demanding the project but also an investment screening organization, a budget-managing organization, a feasibility assessment institution and many other related organizations participate in the project and a lot of decisions arisen from the project operation are made on the basis of construction expenses calculated for relevant stages. And estimation of rational construction expense is also critical for designers in order to create design within the fixed budget simultaneously with securing the quality and efficiency of structures to the maximum. Therefore this research suggested an improvement process to analyze problems in current construction expense management process and to administer the construction expenses effectively.

A prediction of construction cost in preparation for construction document is calculated in compliance with the unit cost in Public construction of korea. This eventually means that the reasonable construction cost of a building can't be determined before construction document phase cost of construction is settled and that the cost of construction is calculated inefficiently because of connection failing between cost management of detailed estimation and information. To improve those problems, therefore, Cost estimating model of structural building elements with approximate quantity survey method is suggested in this research. The model predict the amount of materials and the cost of construction on the basis of historical similar cases. In the direction of data analysis of this research, ratio statistics value is put to practical use to fit into the peculiarities of approximate estimate of each work trade on the basis of actual data amount of materials of historical cases. In addition, the construction phase is connected through the result of a approximate estimate sorted by elements, details work trade.

When managers predict exact construction cost at early stage and design phase, they can reduce construction cost in a more efficient way than to predict at construction stage. But present of public construction cost estimation and management almost after the construction documents design phase. Therefore, construction cost management in the early stage and schematic design phase to generally use approximate estimating is not correct. Accordingly, this study analyze problem of current cost estimating method and a concrete cost plans make using case information of actual cost to analyze in schematic design phase. Possible to check going on the suitable design, this study conducts the preliminary research for the development of cost estimating model.